I think it kinda sounds like a mess waiting to happen....too bad. They were designed in conjuction with some German tube guy who was building tube Mutron's (!) at the time. If you look you can find pictures of his stuff somewhere on the Harmony Central site from Music Messe in Frankfurt; cool stuff. Maybe this box would be good, I don't know and if the samples are any indication I'd say no.
Sound bytes here; http://buzzfox.com/el-zipper-swf.html

Ahhh, Carefull lads! The Zipper and the TUBE Zipper are different pedals. Check out harmony central for reviews on both. The Zipper (not currently reissued) seems to come out best judging by popular opinion. I've downloaded mp3's of the tube zipper at www.ehx.com and it sounds like it can do some really cool stuff. No samples for bass though. The sweep range on this thing seems to be amazing, like a micro-synth. If the link thing works check it out, but be warned, it makes the sub on my computer system flap at the end!